1. Field of the Invention
The present invention is directed to a monomolecular electronic device. In particular, the present invention is directed to a monomolecular transistor and monomolecular digital logic structures utilizing a molecular transistor to provide switching and power gain. More particularly, the present invention directs itself to the adding of a molecular gate structure to a molecular diode, where the diode is also chemically doped. The molecular gate structure is formed by yet another insulator group bonded to the molecular diode in proximity to a respective dopant group that is influenced by a potential applied externally to the gate structure. A current conducting complex is bonded to this second insulating group so that it can be charged by an external voltage to influence the intrinsic bias of the diode and thereby switch the device xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d. Still further, this invention is directed to a molecular transistor wherein the power required to control the switching is substantially less than that which is being switched, and therefore the transistor exhibits power gain. The present invention also pertains to monomolecular logic gates constructed from combinations of monomolecular diode-diode logic and monomolecular inverters having power gain.
2. Prior Art
For the past forty years, electronic computers have grown more powerful as their basic sub-unit, the transistor, has shrunk. However, the laws of quantum mechanics and the limitations of fabrication techniques soon may prevent further reduction in the size of today""s conventional field-effect transistors. Many researchers project that during the next ten to fifteen years, as the smallest features on mass-produced transistors shrink further from their present approximate width in the range of 100 nanometers to 250 nanometers, the devices will become more difficult and costly to fabricate. In addition, they may no longer function effectively in ultra-densely integrated electronic circuits. In order to continue the miniaturization of circuit elements down to the nanometer scale or even to the molecular scale, researchers have been investigating several alternatives to the solid-state transistor for ultra-dense circuitry. However, unlike today""s FETs, which operate based on the movement of masses of electrons in bulk matter, the new devices take advantage of quantum mechanical phenomena that emerges at the nanometer scale.
There are two broad classes of nanoelectronic switches and amplifiers.
(a) solid-state quantum-effect and single electron devices, and
(b) molecular electronic devices.
Devices in both classes take advantage of the various quantum effects that begin to dominate electron dynamics on the nanometer scale. Despite the novelty of the designs of solid-state quantum-effect and single electron devices, researchers already have been able to develop, fabricate, and employ in circuitry several promising new device types by building upon fifty years of industrial experience with bulk semiconductors. Such solid-state quantum-effect devices change the operating principles for ultra-miniature electronic switches, but they still bear the difficult burden of relying on nanometer-scale structures that must be xe2x80x9ccarvedxe2x80x9d out of amorphous or crystalline solids.
Molecular electronics is a relatively new approach that would change both the operating principles and the materials used in electronic devices. The incentive for such radical change is that molecules are naturally occurring nanometer-scale structures. Unlike nanostructures built from bulk solids, molecules can be made identically, cheaply, and easily, as will be needed for industrial scale production of ultra-dense computers. Two of the significant challenges to overcome are (1) to devise molecular structures that act as electronic switches having gain, and (2) to combine those molecules into a more complex circuit structure needed for computation and control applications, as well as providing gain in those applications, so that the devices thus produced have a usable xe2x80x9cfan outxe2x80x9d.
As is known, a diode is a two-terminal switch, which can turn a current xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d. Two types of molecular-scale electronic diodes that have been developed recently, are:
(a) rectifying diodes, and
(b) resonant tunneling diodes.
Both types of diodes rely on the application of an external bias voltage to drive electrons through one or more energy barriers when the externally applied potential reaches a predetermined magnitude.
A molecular resonant tunneling diode (RTD) has been developed, which takes advantage of energy quantization in a manner that permits the amount of voltage bias across the source and drain contacts of the diode to switch xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d electron current traveling from the source to the drain. Depicted in FIG. 1A, is a molecular resonant tunneling diode that has been synthesized by James M. Tour and demonstrated by Mark A. Reed in 1997. Structurally and functionally, the device is a molecular analog of the much larger solid-state RTDs that for the past decade have been fabricated in quantity in III-V semiconductors. Based upon a molecular conductive wire backbone, as shown in FIG. 1A, Reed""s and Tour""s polyphenylene molecular RTD 11xe2x80x2 is made by inserting two aliphatic methylene groups 16xe2x80x2 into the molecular conducting wire 12 on either side of a single benzene ring 13xe2x80x2. Because of the insulating properties of the aliphatic groups 16xe2x80x2, they act as potential energy barriers 30 and 32 to electron flow, shown in the energy diagrams of FIGS. 1B and 1C. They define the benzene ring 13xe2x80x2 between them as a narrow, approximately 0.5 nanometer, xe2x80x9cislandxe2x80x9d through which electrons must pass in order to traverse the length of the molecular wire.
As illustrated in FIG. 1B, if the bias across the molecule produces incoming electrons with a kinetic energy, that differs from the energies of unoccupied quantum levels available inside the potential well on the island, the current does not flow. The RTD is switched xe2x80x9coffxe2x80x9d. However, if the bias voltage is adjusted so that the kinetic energy of the incoming electrons aligns with that of one of the internal energy levels, as shown in FIG. 1C, the energy of the electrons outside the well is said to be in resonance with the allowed energy inside the well. Under that condition, current flows through the device and that is said to be switched xe2x80x9conxe2x80x9d.
In French Patent Publication #2306531 there is disclosed a molecular switching device that may be used for amplification. Conductors are formed by chains of adjacent double links or bonds between the rings thereof, and are terminated in two dissipating regions. However, the referenced device has a principal of operation that is generally analogous to bulk effect semiconductors, rather than an effect that can only be realized in individual molecules, wherein, for example, the effects of at least one dopant are reversed by an externally applied potential.
In PCT Publication #WO97/36333 there is disclosed a tunneling device which makes use of control electrodes to control the tunneling current flowing between the input and output of the device. The device is based on the principle of controllable correlated electron tunneling. The reference also suggests the use of such a device to construct single-electron logical circuits.
A monomolecular electronic device is provided that includes a plurality of molecular conducting wires chemically joined together with at least one insulating group. At least one of the plurality of molecular conducting wires is chemically joined to a dopant substituent to form an intrinsic bias across the insulating group. A second insulating group is chemically coupled to the molecular conducting wire that is joined to the dopant substituent. A current conducting complex is chemically joined to the second insulating group to form a single molecule that exhibits power gain. The second insulating group is disposed in sufficient proximity to the dopant substituent to influence the intrinsic bias with a potential applied to the current conducting complex. The monomolecular electronic device of the present invention may be provided in the form of an inverter circuit wherein a third insulating group is chemically bonded to a second of the plurality of conducting wires, and a plurality of joined aromatic ring structures are chemically bonded to the third insulating group.
Looking at the invention from another aspect, such is directed to a monomolecular electronic device having power gain. The monomolecular electronic device includes at least one molecular conducting wire having a plurality of joined substantially identical aromatic ring structures. At least one first insulating group bonded between a respective pair of the aromatic ring structures establishes two sections of the molecular conducting wire, a first of the sections being coupled to a first electrical contact, and a second of the sections being coupled to a second contact. At least one of the two sections is doped to form at least one of an electron donor site and an electron acceptor site. A molecular gate structure is chemically bonded to one of the first and second sections in sufficient proximity to the dopant to influence by means of a potential applied to the gate structure an intrinsic bias formed between the first and second sections by the dopant. The molecular gate structure is coupled to a third contact for coupling to a source of the applied potential.
From yet another aspect, the present invention is directed to a monomolecular transistor that includes a polyphenylene-based conducting wire having a plurality of joined molecular ring structures, and at least one insulating group bonded between a respective pair of the molecular ring structures to establish two sections of the conducting wire. The monomolecular transistor also includes a first dopant group bonded to at least one molecular ring structure of one section of the conducting wire to form a respective electron donor site. A second dopant group bonded to at least one molecular ring structure of the other section forms an electron acceptor site. A second insulating group is chemically bonded in proximity to one of the first and second dopant groups, and a current conducting complex is bonded to the second insulating group for coupling an electric charge thereto for modifying an intrinsic bias formed by the first and second dopant groups.
From a further aspect, the present invention is directed to a monomolecular electronic device formed by a molecular diode having at least one barrier insulating group chemically bonded between a pair of molecular ring structures to form a pair of diode sections. At least one dopant group is chemically bonded to one of the pair of diode sections. A molecular gate structure is chemically bonded to the one diode section to which at least one dopant group is chemically bonded for influencing an intrinsic bias formed by the at least one dopant group.
It is therefore an object of the present invention to provide a monomolecular switching device that exhibits power gain.
It is a further object of the present invention to provide an electronic switching device with power gain by the addition of a gate structure to a doped molecular diode to form a single molecule which functions as a transistor.
It is still another object of the present invention to provide a monomolecular transistor circuit that functions as an inverter.
Further, it is an object of the present invention to provide Boolean logic functions by the joining together of molecular diode-diode logic structures with a molecular inverter to provide particular Boolean functions and simultaneously thereby provide power gain.
These and other advantages and novel features of the invention will become apparent from the following detailed description when considered in connection with the accompanying drawings.